This abstract class provides the base class from which all
code-access and identity permission classes are derived. It
implements the IPermission,
IStackWalk, and
ISecurityEncodable interfaces, but only provides
concrete implementations of the IStackWalk methods
(Demand( ), Assert( ),
Deny( ), and PermitOnly( )),
leaving implementation of the other interface methods to the derived
classes. The staticRevertAll( ),
RevertAssert( ), RevertDeny( ),
and RevertPermitOnly( ) methods remove existing
stack walk overrides of the appropriate type from the
caller's stack frame.